Journal
JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL
Volume 315, Issue 1, Pages 43-50Publisher
ELSEVIER
DOI: 10.1016/j.molcata.2009.08.028
Keywords
Vanadium oxide; Activated carbon; Alcohol oxidation; Raman; X-ray absorption; XPS; ESR
Categories
Funding
- AcRF [2 ARC 13/07]
- NUS [C-380-003-003-001]
- A*STAR/MOE [3979908M]
- A*STAR [12 105 0038]
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Vanadium oxide catalysts supported on activated carbon (V/AC) with V loadings ranging from 1 to 20wt.% were prepared by a wet-impregnation method. Various physicochemical characterization techniques, including nitrogen physisorption, X-ray diffraction (XRD), Raman spectroscopy, X-ray absorption (XANES and EXAFS), X-ray photoelectron spectroscopy (XPS), and electron spin resonance (ESR), were employed to understand the nature of vanadium species on activated carbon. The results revealed that vanadium oxide mainly existed in a highly dispersed state for 10 wt.% or less vanadium loadings: a large amount of vanadium resulted in aggregated microcrystalline phase. Vanadium species on activated carbon surface showed a similar local coordination structure to that of NH4VO3 with a distorted tetrahedral symmetry at low vanadium loadings, whereas octahedral coordination was dominant at high vanadium loadings (>10wt.%). All V/AC samples showed V5+ as the major oxidation state. Nevertheless, V4+ centered in a distorted tetrahedral symmetry could be detected at a vanadium loading greater than 4 wt.%. The catalytic activity for the benzyl alcohol oxidation largely depended on the dispersion, oxidation state, and local coordination of vanadium oxides on activated carbon. Highly dispersed vanadium (5+) species with a distorted tetrahedral coordination were postulated to account for the excellent catalytic performances of V/AC catalysts (TOF=39.1 h(-1)). (C) 2009 Elsevier B.V. All rights reserved.
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